16 THE FALL OF THE BIRTH-RATE 



Now we know that this figure must be too low, for 

 we have seen from Table III that the average age of 

 the married women under 45 was appreciably higher 

 in 1911 than in any of the years preceding it. So 

 that the fall in the fertility of married women, apart 

 from any effect of changes in age, was certainly less 

 than 31-9 per cent. But how much less? Can we get 

 any measure of this ? 



If, at the time a birth was registered, the age of the 

 mother had to be given, there would be no great 

 difficulty. We could see, at each census year, or for 

 an average of years round each census year, how 

 many births there had been per thousand wives aged 

 15 but under 20, 20 but under 25, 25 but under 30, 

 and so on for every age-group, and we could compare 

 the fertilities at each separate age-group from census 

 to census. If we wanted to obtain some sort of sum- 

 mary or average figure for wives of all ages, we could 

 take some fixed arbitrary numbers of wives at each 

 age as a standard say the numbers at the census of 

 1911 and calculate the numbers of births there 

 would have been to such wives at the fertility rates 

 for the several age-groups given by the birth-records 

 of 1851, 1861, 1871, etc. These figures, expressed as 

 a proportion per thousand of the population would 

 have given us what are termed "standardised fertility 

 rates " or " standardised birth-rates " rates which are 

 appreciably freed from the effect of changing num- 

 bers and ages of the married women, and are there- 

 fore measures of changing fertility. The process is 

 analogous to the process of "standardisation" of 

 death-rates which has long been in use. 



But we have not got, in this country, the ages of 

 the women at the birth of their children. We must 

 therefore use some other process, and again a method 

 already in use for death-rates is available, sometimes 



